1// Copyright (c) 2012 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// This module provides a way to monitor a file or directory for changes.
6
7#ifndef BASE_FILES_FILE_PATH_WATCHER_H_
8#define BASE_FILES_FILE_PATH_WATCHER_H_
9
10#include "base/base_export.h"
11#include "base/callback.h"
12#include "base/files/file_path.h"
13#include "base/macros.h"
14#include "base/memory/ref_counted.h"
15#include "base/single_thread_task_runner.h"
16
17namespace base {
18
19// This class lets you register interest in changes on a FilePath.
20// The callback will get called whenever the file or directory referenced by the
21// FilePath is changed, including created or deleted. Due to limitations in the
22// underlying OS APIs, FilePathWatcher has slightly different semantics on OS X
23// than on Windows or Linux. FilePathWatcher on Linux and Windows will detect
24// modifications to files in a watched directory. FilePathWatcher on Mac will
25// detect the creation and deletion of files in a watched directory, but will
26// not detect modifications to those files. See file_path_watcher_kqueue.cc for
27// details.
28class BASE_EXPORT FilePathWatcher {
29 public:
30  // Callback type for Watch(). |path| points to the file that was updated,
31  // and |error| is true if the platform specific code detected an error. In
32  // that case, the callback won't be invoked again.
33  typedef base::Callback<void(const FilePath& path, bool error)> Callback;
34
35  // Used internally to encapsulate different members on different platforms.
36  class PlatformDelegate : public base::RefCountedThreadSafe<PlatformDelegate> {
37   public:
38    PlatformDelegate();
39
40    // Start watching for the given |path| and notify |delegate| about changes.
41    virtual bool Watch(const FilePath& path,
42                       bool recursive,
43                       const Callback& callback) WARN_UNUSED_RESULT = 0;
44
45    // Stop watching. This is called from FilePathWatcher's dtor in order to
46    // allow to shut down properly while the object is still alive.
47    // It can be called from any thread.
48    virtual void Cancel() = 0;
49
50   protected:
51    friend class base::RefCountedThreadSafe<PlatformDelegate>;
52    friend class FilePathWatcher;
53
54    virtual ~PlatformDelegate();
55
56    // Stop watching. This is only called on the thread of the appropriate
57    // message loop. Since it can also be called more than once, it should
58    // check |is_cancelled()| to avoid duplicate work.
59    virtual void CancelOnMessageLoopThread() = 0;
60
61    scoped_refptr<base::SingleThreadTaskRunner> task_runner() const {
62      return task_runner_;
63    }
64
65    void set_task_runner(scoped_refptr<base::SingleThreadTaskRunner> runner) {
66      task_runner_ = std::move(runner);
67    }
68
69    // Must be called before the PlatformDelegate is deleted.
70    void set_cancelled() {
71      cancelled_ = true;
72    }
73
74    bool is_cancelled() const {
75      return cancelled_;
76    }
77
78   private:
79    scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
80    bool cancelled_;
81  };
82
83  FilePathWatcher();
84  virtual ~FilePathWatcher();
85
86  // A callback that always cleans up the PlatformDelegate, either when executed
87  // or when deleted without having been executed at all, as can happen during
88  // shutdown.
89  static void CancelWatch(const scoped_refptr<PlatformDelegate>& delegate);
90
91  // Returns true if the platform and OS version support recursive watches.
92  static bool RecursiveWatchAvailable();
93
94  // Invokes |callback| whenever updates to |path| are detected. This should be
95  // called at most once, and from a MessageLoop of TYPE_IO. Set |recursive| to
96  // true, to watch |path| and its children. The callback will be invoked on
97  // the same loop. Returns true on success.
98  //
99  // Recursive watch is not supported on all platforms and file systems.
100  // Watch() will return false in the case of failure.
101  bool Watch(const FilePath& path, bool recursive, const Callback& callback);
102
103 private:
104  scoped_refptr<PlatformDelegate> impl_;
105
106  DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
107};
108
109}  // namespace base
110
111#endif  // BASE_FILES_FILE_PATH_WATCHER_H_
112